Separation and purification of hydrocarbons



Dec. 18,1945.

J. A. PATTERSON Filed Jan. l, 1943 lill i dwniwns WWINN A .I. LUORORR 22.2502" Patented Dec. 18, 1945 ,UNITED STATES .PAT-ENT vOFFICE SEPARATION AND PURIFICATION O'F HYDROCARBONS v John A. Patterson, Westfield, N. J., asslgnor to Standard Oil Development Company, a corporation of Delaware Application January 1, 1943, Serial N0. 470,977

7 Claims. (Cl. 260--681;5)

This invention relates to the treatment ol mixtures of hydrocarbons of the C3 to Cc range to effect the separation and puriiication of parafiins, mono-oleflns and diolens. The invention relates particularly to the separation'of dioleflns from their admixture with other hydrocarbons in the products of the treatment of petroleum fractions and also to thev purication of dioleiins.

Great importance today is attached to the preparation of synthetic products from the lower molecular weight unsaturated hydrocarbons. Such important products as synthetic rubber and alcohols are being prepared by processes employs ing unsaturated -hydrocarbons as raw materials.

The development of such synthetic processes is, however, largely determined by the availability of the respective unsaturated hydrocarbons ina high degree of purity. Fractional distillation as a means of-separating the unsaturated hydrocarbons from complexmixtures containing hydrocarbons of about the same molecular weight is completely unsatisfactory because of the closely related physical properties and the difficulties involved in preventing polymerization. It' has been vproposed to combine a fractional distillation with extractive distillation as a means for separating the various unsaturated hydrocarbons from the' saturated hydrocarbons. Such processingl is clearly limited to the capacity of processing based upon such a combination. The present invention is a further advance in the separation of individual hydrocarbons Afrom complex mixtures.

In fractional distillation separation of components ismade upon the basis of their normal va- Por pressures in the presence of other constituents of the hydrocarbon mixture. In extractiva distillation, the separation of groups of compounds is made on the .basis of the relative volatilities of various groups of compounds in the presence of an added solvent. The present invention is concerned with extractive distillation combined with a selective solvent extractionen carbons relative to parafiins are lowered andthe relative volatilities of the dioleiins are lowered to a greater extent than those of the mono-olens. In suchv a system the relative volatility of two compounds of about the same degree of unsatu-l ration such as trimethylethylene and pentene-l ischangedto about the same extent. On the other hand, extraction of a close-boiling hydrocarbon mixture witha selective solvent such as a. cuprous complex salt solution results inthe absorption selectively of groups of compounds about the same molecular Weight in relation to their structure and to a lesser extent upon their degrec of unsaturation. Thus, straight chain hydrocarbons are, in general, more soluble in these solutions than the corresponding .branched compounds, and also, in. general, the higher the degree of unsaturation and the lower the molecular weight, the greater the solubility. For example,

pentene-l is more readily extracted from a complex mixture than trmethylethylene by a selective solvent of the type of cuprous acetate dissolved in pyridine solution, since such a solution has a marked selective solvency for the straight-chain olens. By a combination, therefore, of selective solvency and extractive distillation, separation can be conveniently made of oleflns from dloletlns on the basis of both structure and degree oi unsaturation.

Any cuprous salt `dissolved in a basic reacting organic nitrogen compound is' advantageous as a selective solvent. Particular basic reacting organic-nitrogen compounds advantageous as solvents for the cuprous salts are' pyridine and the amines. The selective solvent of this invention is advantageously employed at temperatures between 30 and `125" F., and preferably at about 90 F. A particularly suitable composition is cuprous acetate dissolved in pyridine-solution.

As an illustration of the invention, the separation of a mixture containing .pentene-l, trimethylethylene and isoprene in addition to other C5 hydrocarbons may be taken. These hydrocarbons have such closely related boiling points that complete separation by fractional distillation, even under high reiiux ratios, is not practical even in the laboratory. When the mixture containing the three hydrocarbons is, however, sub- A jected to extractive distillation in which aqueous pyridine is used as the solvent, pentene-l may be readily separated in the distillate material. Trimethylethylene may also be separated from isoprene by extractve distillation. However, in the labsence of the solvent, isoprene has a normal volatility greater than that of trimethylethyienf.

viating intermediate solvent removal.

sothat the difference in volatility in the presence of the solvent is not suiiicient to' permit ready separation. When the residue, however, from the extractive distillation is extracted with cuprous acetate pyridine solution, the isoprene is selectively absorbed, so that the undissolved portion contains essentially all of the trimethyletwlcomplex hydrocarbon mixture with the selective solvent of this invention previous to extractive distillation. In other cases, it may be advantageous to separate a. complex mixture rst on the basis of fractional distillation and then to subject a particular fraction to the selective solvent extraction and extractiva distillation according to this invention. The particular order is determined largely by the content of the particular unsaturated materials dissolved by the selective solvent and thus the economics of the processing, according to a particular order.

A special feature of the combination extractive distillation and selective solvent extraction is that, if the same basic nitrogen compound, such as pyridine, is employed as the solvent in both steps of such processing, there is the convenience of ob- Eor example, when the cuprous salt dissolved in pyridine is employed as the selective solvent in the first step of such processing, 'the hydrocarbons regenerated from the extract fractions contains a considerable quantity of pyridine. Such material may then be directly fed to the extractive distillation system |by adjusting Ithe solvent circulation in that operation. When the order of processing is re- 'versed, .the step of freeing the distillate product from the extractive distillation completely of pyr-I idine is clearly unnecessary; The cuprous saltpyridine extraction operation may be readily adjusted to compensate for the pyridine content of the feed to the solvent extraction treatment.

In order tov illustrate the invention more specically, the following example is presented. The numerals given in the description refer to the accompanying drawing, in which-is outlined a suitable lay-out of proceing equipment. In thisexample, the feed supply is a debutanized renery cracked stock of boiling range from 60 F. to400f F. obtained from high temperature operation. that is, a stock consisting essentially of C to Co hsv-,- drocarbon.- 'I'hc illustration is taken of the extraction of transpiperylene from this stock.

The feed is introduced near the bottom of tower I through line 2. 4Tower I is any form of suitable equipment for eifecting` countercurrent liquidliquid extraction Thus, tower I may be a tower packed with Raschig rings or other contacting devices. The feed. passes upwards through the tower countercurrently to a stream of cuprous acetate-pyridine solution introduced at the top of the tower through line 5. During the countercurrent operation, the cuprous acetate-pyridine solution extracts from' the feed the content of transpiperylene and other dioiefins'and straight chain olefins and leaves undissolved parailinsand branched chain oleflns. The extract material is removed through line 4 and passes to the stripping tower II. The undissolved portion of the feed, together with some dissolved pyridine. is

withdrawn .through line 3 for subsequent treatment for recovery of. the pyridine.

.'llower II may be any suitable type of distillation equipment, such as a bubble plate tower containing .about 10 plates. The tower is provided with a heating means I6. In the tower II the cuproils solution is stripped of its hydrocarbon content. The stripped cuprous acetate pyridine solution is withdrawn at the base of the tower through line I4, cooled in heat exchanger I1 and recycled through line 5 to tower I. The hydrocarbon distillate containing some pyridine is passed .through line I3 to the extractive distillation tower 2i.

Tower 2l is any suitable type of distillation unit, but preferably of bubble plate construction havsupplied throughl line I3 is introduced near the middle of the tower. Pyridine-water as lthe exrtractive solvent is introduced through line 24 near the plates of three volumes of solventi-.o one volume of hydrocarbon in the region .between the solven-t inlet '24 and the side stream withdrawal line 32. In the Atower-below the level of the line 32 connection, the solvent `is concentrated as it passes toward the base of the tower so that relatively pure solvent is withdrawn at the base. The solvent is cooled in heat exchanger 22 and recycled through line 24 to tower 2I. In the presence of Ithe solvent the relative volatilities of the C5 hydrocarbons are such that the straight chain olefins are taken overhead through line 23 as distillate, while the dioleiins together with some PYT- idine and water are withdrawn through line 32. The normal olefin distillate withdrawn through line 23 is condensed in equipment 21 and collected in equipment 28. A portion of the condensate is returned as reflux to the top of tower 2l through line 25, while the remainder is withdrawn through line 42 for subsequent treatment.

The 'diolefln solvent vapor mixture removed from the tower through line 32 is introduced into fthe side stream tower 3I.- Tower 3| may be of 45 any suitabletype for eecting distillation, but

preferably of bubble type construction similar to tower 2 I except as to having only about 10 plates.

The vapor feed through line 32 furnishes .the

heat required to operate the tower 3l. In the 50 tower 3i the diolens are freed of most of the (pyridine and water. The pyridine and water are returned from the .base of the tower Il through line 34 to tower 2|.

e distillate from tower )I consisting of diole- 55 uns and small amounts of pyridine 4and water is withdrawn through line I3 and condensed in equipment 31. The condensate is collected in the drum I8. Sufiicient condensate from the drum l! vis reuxed to the tower II throughv line a! to maintain the proper operating conditions in tower 3|. The remainder ofthe condensateis withdrawn from theidrum I8 through line B2 for subsequent treatment.

The concentrated Adioleilns separated as a 65 stream through line 52 are introduced near -the base of extraction tower 6I. Tower II may be lany suitable device for countercurrentliquid-liquid contacting device, preferably a tower packed The' dioleiin stream passes with Raschig rings. upward through the tower countercurrentto a stream of water introduced near the top through line 5l.V The water extractsthepyridine from the ,dioleiin mixture, the latter passing out of the ing from 50 to'60 plates. The vapor feed stocky top of tower Il through line 63 for further treatu ment in the pin'iiication cftranspiperylene. The

water extract is withdrawn atvthe base of the tower through line 54 for subsequent treatment. 'I'he undissolved parain andbranched chain oleiln stream which is withdrawn from tower- I through line 3 is combined with the normal olen distillate fraction stream' passing through line 42.

' The combined stream is introduced into tower 4| near its base. Tower 4I is similar to tower 5l. I

Water is introduced' near the top oi.' the tower through line 45 and ilows downward countercurrent tothe olen-'paraiiin mixture and removes from the mixture the dissolved pyridine. The paramn olefin stream is withdrawn at the top of tower 4l through line 43 and discarded from the system. The water extract of pyridine is withdrawn through line 44 at lthe baseof the tower.

'Ihe .water extracts from the towers and 5| which are withdrawn through lines 44 and 54 respectively are combined and passed through line to the solvent recovery tower 6l. Tower 6| may be any suitable type oi' distillation unit, but

is preferably of'bubble plate construction containingabout l0 lbubble cap plates. The base of the tower is furnished with heating means B6.

The overhead product of the tower systemA con-- sista of essentially pure water and is withdrawn through line, condensed in equipment 61 and cooled in drum 6l. A portion or the distillate in Il is returned as reflux through line 85 in order to maintain the proper operating conditions in tower 8l. The remainder is withdrawn through line '49 and may be either discarded or recycled through lines 45 and 55 to towers 4I and 6l respectively. The bottoms from tower Il consisting o! yhighly concentratedpyridlne is withdrawn through -llne C4 and added-to either the recycling 'what is cimmed is:

1. The process of separating an individual un- I saturated hydrocarbon of the C: to .Ca range from a complex hydrocarbon mixture, which comprises is employed as extractive solvent.

2. The process according to claim 1, in 4which the cuprous complex salt solution is cuprous acetate in pyridine.

3. The process according to claim 1, in-which the cuprous complex salt solution is cuprous acetate in aqueous pyridine.

4. The process according to claim 1, in which the cuprous complex salt solution is cuprous acetate in an amine.

cuprous acetate-pyridine solution contained in' l circulating in line 24 to make up for the solvent carried out of thetowers l and 2l in the products. 'I'he operation of tower 81| may be adjusted by line l onto the recycling pyridine water solvent means of control of the heat supplied through f equipment Il and the reilux supplied through line il. so that the pyridineremoved throughline' I4' will contain proper concentration of water for combination with the solvent solutions used in the solvent extractionA and extractiva distillation op-` Y erations.

5. The process of separating an individual Cs d unsaturated hydrocarbon from a mixture of Cs' to C hydrocarbons, which comprises treating the mixture with cuprous acetate in a basic reacting organic nitrogen compound, separating the extract and raiilnate solutions, removing the cuprous acetate from the extract solution and the basic reacting organic nitrogen compound from the raffinate solution, and subjecting the resultant products to an extractive distillation in which said basic reacting organic nitrogen compound is employed as extractive solvent.

6. The processvaccording to claim 5, in which the individual C5 unsaturated hydrocarbon separated from the mixture .of Cs to Cn hydrocarbons is isoprene Aand in which the basic reacting organic-nitrogen compound is pyridine.

7. The. process according to claim 5, lin which the individual Cs unsaturated hydrocarbon separated from the mixture of Cato Cn hydrocarbons is trans-piperylene and in which the basic 'reacting organic-nitrogen compound is pyridine.-

JOHN A. PATTERSON. 

